1. Field of the Invention
This invention relates generally to a vehicle stability control system and, more particularly, to a vehicle stability control system that employs driver skill recognition to enhance the control.
2. Discussion of the Related Art
Modern vehicles sometimes incorporate active vehicle control systems. One such system is known as a vehicle stability enhancement (VSE) system that assists the vehicle operator in providing vehicle handling on surfaces such as wet or uneven pavement, ice, snow or gravel. The VSE system typically senses wheel skid based on inputs from a wheel speed sensor, a steering angle sensor, a vehicle speed sensor and a vehicle yaw rate sensor. The VSE system uses these inputs to reduce engine torque and apply differential braking to help maintain the vehicle travel along the intended path.
Additionally, active chassis control systems have been emerging in the art that are used in combination with VSE systems. The chassis control systems typically include differential braking control, real-time suspension damping, rear-wheel steering and active front steering control. With the capability of controlling chassis dynamics in real time, the active chassis control systems can be used to enhance the vehicle handling performance.
Another active vehicle control system is known as an active front steering (AFS) system that provides automatic front-wheel steering. AFS systems typically employ a steering actuator system that receives an operator intended steering signal from a hand-wheel sensor, a vehicle speed signal and a vehicle yaw rate signal, and provides a correction to the operator steering signal to cause the vehicle to more closely follow the vehicle operator's intended steering path to increase vehicle stability and handling. The AFS system is able to provide steering corrections much quicker than the vehicle operator's reaction time, so that the amount of operator steering is reduced. The AFS system provides a more direct vehicle steering under normal road conditions at low and medium speeds, reducing operator steering effort. The AFS system also may help to increase vehicle agility in city traffic or during parking maneuvers. The AFS system also provides less direct vehicle steering at higher vehicle speeds.
Vehicle driver skill levels come in a wide range. For novice or young drivers, it is desirable that the vehicle stability enhancement provide stability control as close as possible to the drivers intended path with minimal vehicle side-slip. However, for experienced or high performance drivers, a certain amount of side-slip is generally desirable because it increases the driving experience and enjoyability and allows more control for vehicle cornering. Therefore, it would be desirable to provide a vehicle stability enhancement system, or other vehicle stability control system, that could adapt to different driving skill levels so that the enhancement system performs suitably for drivers of all skill levels.